LAUSR

The effect of loading alkaline earth metal oxides on sulfated alumina-zirconia (S/AZ), as a nanocatalyst in esterification of oleic acid (OA) and transesterification of waste cooking oil (WCO) was experimentally investigated. S/AZ modified by calcium (S/Ca–AZ), magnesium (S/Mg–AZ), strontium (S/Sr–AZ) and barium oxides (S/Ba–AZ) were synthesized by solvent-free method and characterized by various methods. Based on the results, zirconia (Z) and S/AZ exhibited less activity in biodiesel production due to their low acidity and basicity while their activities were clearly increased by loading alkaline earth metal oxides. Among the samples, S/Ba–AZ shows the highest activity in both esterification and transesterification reactions, followed by S/Mg–AZ, S/Ca–AZ, and S/Sr–AZ, respectively. However, evaluating the activity of catalysts in second uses as an important factor for industrial application of a catalyst shows that, although the activity of all samples decreases, S/Ca–AZ has the least deterioration in activity. This can be related to its small particle size (below 15 nm), and well bonding of the calcium oxides with other metal oxides and sulfate groups which eliminates the leaching of active phases. Results confirm that S/Ca–AZ can be chosen as the most appropriate nanocatalyst with high activity and stability for biodiesel production from low-cost feedstock.